An image forming apparatus for forming a dot image is generally applied in a dot-image output device such as a laser-beam printer and a CRT. For example, the laser-beam printer employs an image exposing system or a background exposing system for forming a dot image by providing ON/OFF controls to laser beams according to inputted bitmap data.
A diameter of the dot is maintained substantially constant at a specified value according to a period of laser-beam emission or according to the power of light during formation of a dot image. Then, generally, the dot image is subjected to smoothing processing according to the type of the dot image or according to the resolution when recording is executed.
In the conventional type of image forming apparatus described above, in addition to maintaining a dot diameter constant at a specified value regardless of a type of an output image, since many cases where characters are reproduced as an output image, a larger diameter of a dot suitable for reproduction of characters has been employed. For this reason, when an output image is characters, an optimal dot image for the above purpose can be formed. However, when an output image is an image or a dot image with open characters or the like, a portion with white dots existing between black dots is compressed according to a distance between the dots due to characteristics specific to an output image, which makes reproducibility of image quality lower.
This type of problem occurs not only in printing with the dot-image output device such as a laser-beam printer, but also in displaying with the dot-image output device such as a CRT.